BEIRUT -- Islamic militants have crushed a tribal uprising against their rule in eastern Syria after three days of clashes in a string of villages near the border with Iraq, killing and beheading opponents along the way, activists said Monday.

The fighters from the al-Qaida breakaway Islamic State control huge areas in eastern and northern Syria and are fighting rival rebels, Kurdish militias and the Syrian army for more territory.

Meanwhile, at least 10 people, including four children and two women, were killed Monday when Syrian forces dropped explosives-filled barrels from a helicopter over the Bab Nayrab district of Aleppo in northern Syria, activists said. Many others were buried under the rubble of buildings, they said.

Syrian President Bashar Assad's army regularly dropped the so-called barrel bombs over populated areas in rebel-held territory. Aleppo, once Syria's commercial capital, has seen heavy fighting since rebels seized part of the city in 2012.

The civil war in Syria, now in its fourth year, has continued to bleed while attention has shifted to conflicts in Gaza and Iraq. The Islamic State group, which consists mainly of foreign fighters, has taken over much of northern and eastern Syria as well as western and northern Iraq.

The group has declared a self-styled caliphate in territory it controls along the Iraqi-Syrian border, imposing a harsh interpretation of Islamic law.

The armed revolt by the Shueitat tribe in the eastern province of Deir el-Zour was the first sign of local resistance by tribesmen to the Islamic State group since its fighters swept into the province.

The Britain-based Syrian Observatory for Human Rights and Turkey-based activist Thaer al-Deiri said Monday that Islamic State group fighters regained control of three villages from the Shueitat tribe after being expelled earlier this month.

The activist group said Islamic State fighters beheaded two tribesmen after they fled to the nearby village of Shaafa. It had no immediate word on other casualties in the area.

Clashes over the past two weeks left more than a dozen people dead.

The clashes in eastern Syria came as Islamic State fighters tightened their siege of a major military air base in the town of Tabqa in the northern province of Raqqa. The air base is the last army position in the Raqqa province that is an Islamic State stronghold.

Rami Abdurrahman, head of the Syrian Observatory for Human Rights, said the militants were bombarding the base with artillery and appears to be preparing to storm it.

In neighboring Lebanon, former Prime Minister Saad Hariri announced he was donating $15 million of his own money for the reconstruction of a border town that was overrun by Syria-based Sunni extremists last week.

Hariri told a visiting delegation from the eastern town of Arsal on Monday that the money would go for the construction of schools, hospitals and other projects. The militants withdrew from Arsal on Thursday after fierce clashes with the Lebanese army that went on for five days.

Information for this article was contributed by Zeina Karam of The Associated Press.

A Section on 08/12/2014